A technique is disclosed in Japanese laid-open patent application Sho 63-153899, now Japanese Patent 1,795,501 issued on Oct. 28, 1993, for insertion and removal of packages with the main power still applied (commercially available power).
A technique is also disclosed in Japanese Laid-open patent application Sho 61-163423, now Japanese Patent 2,022,376 issued on Feb. 26, 1996 for battery backup of device packages.
Further, technology is also known for power supply methods for insertion and removal as in Japanese laid-open patent application Hei 5-46281, for which no examination was requested, in a method which separately supplies power to package power supplies by hot-line insertion and removal; and to package power feed systems not having hot-line insertion and removal.
These prior technologies do not take into account hot-line insertion and removal of packages while power is being supplied by a battery backup and also do not adequately consider fluctuations in the power supply voltage during insertion and removal of the package within the power feed system.
In this prior technology, consideration was not given to hot-line (in other words with power still applied) insertion and removal of packages mounted with storage elements for battery backup in the storage devices of computer systems backed up by a battery.
Some possible reasons for non-use of hot-line insertion and removal are that maintenance is generally performed on the computer hardware and software only after turning off the power to shut down the computer system. Another main reason is that both the computer system and the storage device were thought to be items capable of being handled only by experts and which required an operator having a specialist's knowledge.
However, peripheral equipment which form basic components of a computer system became more reliable so that larger operations without shutdowns came to be expected. Stronger demands were made for replacement of programs, and collection and maintenance of data in the computer systems not subject to shutdowns. The performance of small-sized computer systems (in other words personal computers) improved, making it necessary for the ordinary individual to be capable of running a computer. Reasons such as listed above caused a demand for technology to allow the replacement or addition of memory packages in computer systems; driven or backed up by batteries without losing the data stored in these memory packages.
Further, the DRAM is rarely used in memory packages having a battery cell backup. The reason being that DRAM devices required a recharge for the memory function and consume more power compared to the SRAM device.
Due to the above circumstances, the inventors therefore developed a storage device to meet the above needs. In their investigation, the inventors discovered that in memory packages with DRAM devices having a self-refresh mode (function to retain only data with an extremely small electrical current compared with normal current consumption) the hot-line insertion-removal failed in computer systems having a battery backup, where insertion/removal of the prior art functioned by means of the connector pin length. The cause of the failure was lack of a control mechanism to switch over to the DRAM self-refresh function.
A current surge that occurred when a memory package was inserted, was found to cause adverse effects on other than the target memory package.
More specifically, when a package was inserted during battery backup, the control circuit for the package being inserted did not function because there was no main power. Accordingly, a current several times that of the current required in a normal battery backup state was drawn for consumption by the DRAM memory mounted in the package inserted with the power applied (hot line) so that the energy in the battery used as the backup was quickly expended and the service life of the backup battery was extremely short. In worst cases, data was lost in memory packages that had a battery backup up to that time.
So, even if the DRAM memory was not utilized, the operation was unsatisfactory since the control circuit for the inserted package did not function, because there was no main power.
Further, if the package was inserted with the main power applied, the resulting current surge caused a large voltage fluctuation in the power supply, adversely affecting other packages and causing malfunctions in the logic circuit. This kind of technical problem could not be resolved simply by isolating the power feed systems in the supply line having the battery backup.
In the prior art technology for hot-line insertion and removal, when supplying one large capacity current package and one small capacity current package from the same (power) feed line, a large power fluctuation will occur when the large current capacity package is removed from the line on which the small current capacity package is installed, causing malfunctions or damage to occur.